1. Technical Field of the Invention The present invention relates to a fuel injection control method and a system in a direct injection type gasoline internal combustion engine, and more particularly, relates to, in a direct injection type gasoline internal combustion engine with a fuel injection valve directly injecting fuel into a combustion chamber of each cylinder, the technique for controlling the injection period of the fuel injection valve.
2. Prior Art Previously, as a direct injection type gasoline internal combustion engine, engines disclosed in JP U HEI 2-20755, JP U HEI 2-20754 and the like, were well known.
In the engine of JP U HEI 2-20755, the period of injection is arranged to be compensated for on the basis of the differential pressure between the fuel pressure and the pressure in a cylinder, and further, the timing of injection is arranged to be compensated according to the fluctuation of the period of injection.
Moreover, in the engine of JP U HEI 2-20754, it is arranged that the injection quantity is determined by finding the real air quantity from the pressure in a cylinder, and that the period of injection corresponding to the injection quantity is compensated on the basis of the differential pressure between the fuel pressure and the pressure in a cylinder and the timing of injection is compensated according to the fluctuation of the period of injection.
In the direct injection type gasoline internal combustion engine, the period of injection is controlled by measuring the time since the start-up timing of injection. However, there is a possibility that the crank angle position of the finishing of injection is largely delayed, and consequently, the injection control is performed at the moment the pressure in a cylinder is higher than the fuel pressure and a back flow occurs at a fuel injection valve.
For example, in a start-up at low temperature, the required injection quantity is large, and further, the fuel pressure is low just after the start-up in a case where an engine drive type high pressure fuel pump is used, so that the period of injection complying with the required injection quantity becomes long. However, there is a possibility that if the rotation speed rises rapidly after the start-up of injection, the crank angle position of the finishing of injection slips into the latter period of a compression stroke because the period of injection and the timing of injection are left to be values suitable for the state of low speed rotation before rising of the rotation speed, and consequently, a state where the injection valve is controlled to open, is continued even when the pressure in a cylinder has come to be higher than the fuel pressure.
Furthermore, in a case where the period of injection is arranged to be subjected to a feedback control on the basis of the fuel pressure detected by a fuel pressure sensor, the period of injection is excessively compensated if the fuel pressure is detected to be lower than the real pressure because of a breakdown of the fuel pressure sensor, and further, in a case where a fuel pump is in trouble and the specified high pressure cannot be obtained, the period of injection is increasingly compensated by the feedback control, and consequently, there is a possibility that the crank angle position of the finishing of injection is delayed, and a state where the injection valve is controlled to open, is continued even when the pressure in a cylinder has come to be higher than the fuel pressure.